Field of the Invention
This invention relates generally to a device used in the manufacture of photographing photosensitive materials such as photographing films and print paper, photo-mechanical process materials, magnetic recording materials such as magnetic recording tapes, or recording materials such as pressure-sensitive copying sheets or heat-sensitive copying sheets. The device floatingly supports and dries an elongated belt-like material (hereinafter referred to as "a web") with air streams in such a manner that the belt like material is not in contact with an air jetting box while the web is being conveyed under low tension. The invention relates particularly to the air jetting box.
A device for continuously conveying a web while floating it with air streams is known in the art. The device has a plurality of air jetting boxes which are disposed above and below the web in such a manner that they are extended in the widthwise direction of the web and juxtaposed in the direction of movement of the web. A typical example of the construction of the air jetting boxes is as shown in FIG. 1A. That is, the air jetting box has an air jetting surface 2. Two air jetting slits 3 are formed in two opposite edge regions of the air jetting surface 2 which are extended in the widthwise direction of a web 9. A variety of constructions have been proposed for the air jetting box (cf. Japanese Patent Application (OPI) No. 100388/1984 (the term "OPI" as used herein meaning an "unexamined published applicaiton"), and Japanese Patent Application Publication Nos. 1256/1985, 1257/1985 and 33740/1985).
However, the above-described device is disadvantageous in that, when a web small in thickness is conveyed, when the device is operated with a small air quantity or when the web conveying speed is increased, the amount of floating of the web is greatly affected by variation of the tension of the web, as a result of which the web is liable to contact the air jetting box to form a defective product.
Furthermore, depending on the distance between the air jetting slits 3 of the air jetting box and the quantity of air jetted from the slits 3, the web is curved upwardly as shown in FIG. 1B or downwardly as shown in FIG. 1C, so that the web is creased.
In the conventional air jetting box, in order to make the air jetting condition uniform over the entire length of air jetting slits 3, the slits must be formed with high accuracy and buffer plates should be provided inside the air jetting box 1. Thus, the conventional air jetting box is intricate in construction and high in manufacturing cost.